The ash content of a paper product, i.e. inorganic substances in the paper product, generally comprises incombustible additives (e.g., papermaking fillers) added during papermaking industry production as well as incombustible substances in pulps. The ash content of a paper product can be measured in accordance with the method recorded in GB/T 742-2008 “Measurement of Ash Content of Papermaking Raw Material, Pulp, Paper and Paper Board” of National Standard of China.
The increase of the specific gravity of ash content of a paper product (especially papermaking fillers) can greatly reduce the papermaking cost.
CN101736656 A discloses a method of papermaking having an increased filler content, comprising the steps of: providing a blend of filler particles, at least one strength additive and cellulose fiber stock, treating the filler particles with a composition of matter, combining the filler particles with the cellulose fiber stock, treating the combination with at least one strength additive, and forming a paper board from the combination, wherein at least 10% of the filler particles are precipitated calcium carbonate and at least 10% of the filler particles are ground calcium carbonate, the cellulose fiber stock comprises a plurality of cellulose fibers and water, and the composition of matter enhances the performance of the strength additive in the paper board.
CN103038419A discloses a method of papermaking having an increased filler content, comprising the steps of: adding a first flocculant to an aqueous dispersion in an amount sufficient to mix uniformly in the dispersion without causing significant flocculation of the filler particles, adding a second flocculant to the dispersion after adding the first flocculant in an amount sufficient to initiate flocculation of the filler particles in the presence of the first flocculant, the second flocculant being of opposite charge to the first flocculant; combining the filler particles with the paper fiber stock; treating the combination with at least one strength additive selected from the group consisting of synthetic strength additives; and forming a paper mat from the combination, the paper fiber stock comprises a plurality of fibers and water, and the initiated flocculation enhances the performance of the strength additive in the paper mat, wherein the strength additive is not starch.
U.S. Pat. No. 8,088,213 B2 discloses a method of preparing a stable dispersion of flocculated filler particles having a specific particle size distribution for use in papermaking processes comprising a) providing an aqueous dispersion of filler particles; b) adding a first flocculating agent to the dispersion in an amount sufficient to mix uniformly in the dispersion without causing significant flocculation of the filler particles, the first flocculating agent being an anionic flocculant and has a reduced specific viscosity (RSV) of at least 10 dL/g, wherein there is no paper fiber present in the dispersion; c) adding a second flocculating agent to the dispersion after adding the first flocculating agent in an amount sufficient to initiate flocculation of the filler particles in the presence of the first flocculating agent, the second flocculating agent being of opposite charge to the first flocculating and being a cationic flocculant; and d) shearing the flocculated dispersion to provide a dispersion of filler flocs having the desired particle size; and e) carrying out steps a) to d) before adding the dispersion of filler flocs to paper fibers.